Fluid circuit heat transfer device for plural heat sources

ABSTRACT

A heat sink or heat transfer device particularly for integrated circuits, uses a phase change working fluid in a cyclic flow path having at least one evaporator that serves multiple heat sources. The evaporator can be an integral vessel made of thermally conductive material to which the multiple heat sources are coupled, preferably at evaporation points that are placed on opposite sides of a fluid reservoir for the liquid phase of the working fluid that feeds the evaporation points via capillary flow through a picking material.

FIELD OF THE INVENTION

The invention relates to a fluid heat transfer loop having circulatingcoolant in an evaporator coupled to a heat source and a condensercoupled to a heat sink spaced from the heat source. More particularlythe invention concerns a thermally-powered heat transfer loop,containing a phase change coolant, with an evaporator that couplesplural heat sources, potentially at different operational temperatures,into a same circulating coolant loop.

BACKGROUND OF THE INVENTION

Thermal energy transfer loops, known as heat pipes, can transfer heatenergy efficiently from a heat source to a sink. Circulation of theheat- transfer coolant in the loop advantageously can be driven simplyby the heat energy that the loop dissipates. In loops having a coolantphase change, from liquid to vapor at an evaporator that is thermallycoupled with the heat source, and from vapor to liquid at a condenserthat has capacity to absorb heat energy, the phase changes store andrelease a portion of the energy being moved. The heat source might be asemiconductor or integrated circuit, for example. The heat sink can be afinned air-heat exchanger for release of heat into the ambient air,another heat exchange fluid or loop, a thermally conductive mass such asa cabinet, etc.

There are design considerations for such heat pipes. The heat pipetypically needs sufficient capacity over a range of operationalconditions to hold the temperature of the heat source below a desiredmaximum temperature. Providing heat transfer capacity may requireefficiency and may dictate criteria such as minimum contact areas and/orcoolant flow rates. The evaporator and the condenser should have closethermal coupling with the heat source and sink, respectively. To moveheat energy, positive temperature differential must be maintained alongthe heat transfer path from the source to the sink. The thermal transferand fluid dynamic characteristics need to convey heat energy over arange of expected temperatures of the source and sink.

Preferably the device is compact and does not interfere unduly withaccess to structures associated with the heat source and sink. Thedevice should robustly resist damage or deterioration. It should carryminimal expense. These design considerations affect one another. Forexample, increases in capacity generally also increase size or expense.What is needed is efficient thermal transfer activity and high thermaltransfer capacity, in a small and inexpensive device.

Heat energy moves when there is a temperature difference betweenthermally related bodies, e.g., heat conductive materials in aconductive, convective or radiant relationship. Advantages are achievedif the temperature differences are arranged to produce phase changes inthe coolant, i.e., cyclic changes of the coolant that store and releaseheat energy. The gaseous and liquid phases can diffuse and flow, whichis potentially useful to move the coolant in one or both directionsbetween the evaporator and the condenser.

The evaporator is heated by the heat source, causing liquid phasecoolant in the evaporator to vaporize. Heat energy from the evaporatoris transferred into the coolant by the phase change. The vapor phasecoolant dissipates, some flowing to the condenser. The condenser ismaintained at a lower temperature than the evaporator. Heat energy iscoupled from the coolant into the condenser, dropping the temperature ofthe vapor coolant. The coolant condenses back to the liquid phase. Theliquid phase coolant is conveyed back to the evaporator, for example bygravity flow, by capillary flow through a wick structure or other means.The cycle repeats.

So long as the condenser has an associated means to carry the heat away,the process continuously transfers heat energy away from the heatsource. The condenser can dissipate the heat energy into a thermal sinksuch as the ambient air, using a finned heat exchanger, alone orassisted by forced air or the like.

The heat pipe structure generally involves a substantially closed,typically vacuum-tight envelope coupling the evaporator and condenser,and the coolant or working fluid. It is possible to rely on gravity flowfrom the condenser to the evaporator if the orientation of the device isassured. Where gravity is not reliable, for example as in portableelectronic equipment, a wick between the condenser and the evaporatorcan provide capillary flow whereby the surface tension of the coolant issufficient to power the return flow of coolant in the liquid phase. Thewick can comprise particulate material adhered to the inside walls ofthe heat exchanger envelope.

When initially charged, the heat pipe envelope is evacuated andback-filled with a small quantity of working fluid, typically enoughliquid coolant to ensure saturation of the wick. The atmosphere insidethe heat pipe assumes an equilibrium of liquid and vapor phases. In theabsence of a temperature difference between the evaporator and thecondenser, the coolant remains more or less stagnant.

Heat energy added at the evaporator generates additional vapor and aslightly higher vapor pressure at the evaporator. Vaporization of thecoolant stores a certain amount of thermal energy in the phase change.The vapor diffuses through the envelope to the condenser. At thecondenser, the slightly lower temperature causes some of the vapor tocondense giving up the stored thermal energy, known as the latent heatenergy of vaporization. The condensed fluid flows back to theevaporator, e.g., driven by the capillary forces developed in the wickstructure. If the thermal energy output of the heat source shouldincrease, and assuming a constant temperature at the condenser (i.e., ifthe temperature difference increases), the rates of vaporization andcondensation increase, and more heat energy is moved. However, heatenergy can be can be moved even at low temperature gradients. The deviceadapts to dissipate heat as necessary. Its operation is driven only bythe heat that it serves to transfer.

It is conventional in cooling integrated circuits for desktop computers,lappets, servers, power regulation devices and the like, to clamp anindividual heat sink device to each integrated circuit or similar loadthat needs to be cooled. This technique contrasts with techniques thatwould couple the heat energy of several devices to one heat sink, forexample typified by audio amplifiers that have several power transistorsmounted to a single massive heat sink. If several heat sources arethermally coupled to the same heat sink, the hotter source(s) heat thecooler one(s) and vice versa. The operating temperature of the coolersources is increased. The temperature gradient, particularly between thehotter source and the ambient, is reduced. Having a lower temperaturegradient reduces the rate of thermal transfer to the ambient, i.e.,reduces efficiency. It would be advantageous to deal with cooling ofsources having different temperatures in a manner that does not simplyaverage their output and instead benefits from the higher temperaturegradient made possible by the higher temperature heat source.

Larger and smaller scale heat pipes are applicable to differentsituations where more or less heat is to be dissipated. The particularcoolant can be chosen and its pressure conditions set so as to obtaincyclic phase changes at nominal operational temperatures. There is achallenge in the case of modern integrated circuit devices such ascomputer desktop and lap top devices, consumer electronics and similarequipment. Such equipment may have multiple digital processors or otherlarge scale integrated circuits, each dissipating energy at a differentbut substantial rate. It is difficult to provide a heat sink heat pipeoptimized for each heat source due to the range of different devices andthe different operational and ambient conditions that may arise.

Moreover, providing a separate heat pipe for each of several heatsources generally requires a volume of air space for convection and/or ablower to force air over the individual heat pipes and possibly throughthe cabinet holding the equipment. What is needed is an efficient way todeal with plural heat sources producing different heat dissipationconditions, while keeping the overall cabinet compact and uncomplicated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a practicalarrangement for dissipating heat from two or more distinct heat sourcesthat potentially produce different levels of heat energy, such as twointegrated circuit packages on a printed circuit board.

It is also an object to couple plural heat sources into one heatexchange loop, but to do so in a manner that tends to allocate heattransfer capacity to each of the loads, rather than permitting thehigher heat load(s) to dominate unduly.

It is another aspect to provide a way for heat loads to share access toa reservoir of coolant associated with the evaporator of a heat transferloop, but to have distinct evaporating areas fed from the reservoir.

Another object is to enable one or more condensers to serve one or moreloads in a single heat transfer loop from a location that need not beimmediately adjacent to the loads.

These and other objects and aspects are met according to the inventionby a heat sink or heat transfer device, particularly for integratedcircuits, using a phase change working fluid in a cyclic flow pathhaving at least one evaporator that serves multiple heat sources. Theevaporator can be an integral vessel made of thermally conductivematerial to which the multiple heat sources are coupled, preferably atevaporation points that are placed on opposite sides of a fluidreservoir for the liquid phase of the working fluid that feeds theevaporation points via capillary flow through a picking material. Thereservoir can comprise one or more recessed wells in the bottom wall ofan enclosure defining the evaporator, each of the evaporation pointsbeing located at a stepped surface adjacent to a well. A variety ofspecific configurations are provide and discussed below, wherein theheat sources are of unequal output, or are asymmetrically arranged, orare provided in arrays of two or more in one area of the evaporator.

In one embodiment, two integrated circuits or other heat source loadsare cooled by an evaporator vessel that bridges over the two loads, thereservoir being provided at a recessed well between the two loads suchthat surfaces defining evaporation points abut the recessed well atstepped edges on the underside of the evaporator vessel. The evaporationpoints are supplied commonly with working fluid in the liquid phase fromthe recessed well. A vapor outlet is placed substantially over therecessed well, thus being positioned such that vapor from bothevaporation points diffuses into the common vapor outlet. The vaporoutlet has a relatively larger diameter compared to a liquid return pathand is coupled in a circulating heat transfer path from the evaporatorto a condenser such as a finned air heat exchanger that releases heatenergy into the ambient air by convection. Condensed working fluid inthe fluid phase is returned from the condenser to the well of theevaporator reservoir by a smaller diameter liquid return line.

The liquid flow can be assisted by gravity, assuming a given orientationof the device, but preferably the liquid flow paths contain pickingmaterial such as sintered or adhered particles or fibers spaced closelyso as to support capillary flow. In this manner the liquid phase workingfluid is returned from the condenser to the reservoir regardless oforientation of the device and the influence of gravity on liquid flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages of the invention, as well as otheraspects and routine extensions of the invention, are apparent from thefollowing detailed description of examples and preferred embodiments, tobe considered together with the accompanying drawings, wherein the samereference numbers have been used throughout to refer to the samefunctioning parts, and wherein:

FIG. 1 is a perspective view of a circulating coolant heat pipearrangement according to a first embodiment of the invention, comprisingtwo evaporator sections for distinct heat sources, sharing a condenser,coolant reservoir and associated structures.

FIG. 2 is an exploded perspective view showing a detail of evaporatorand coolant reservoir structures according to the embodiment of FIG. 1.

FIG. 3 is a longitudinal cross-sectional view the embodiment shown inFIG. 2 as assembled.

FIG. 4 is a partly sectional elevation view of the embodiment of FIG. 1.

FIG. 5 is an elevation view corresponding to FIG. 4.

FIG. 6 a is a combined elevation and plan view of an arrangement of heatsources coupled to an evaporator as in FIG. 1.

FIG. 6 b is a combined view as in FIG. 6 a, showing an alternativearrangement wherein the heat sources and evaporator are configuredasymmetrically.

FIG. 6 c is a plan view of a further alternative in which severalevaporator legs radiate from a central reservoir area.

FIG. 6 d is a plan view of an alternative in which plural heat sourcesare grouped in different areas of a shared symmetrical evaporator andshared reservoir arrangement.

FIG. 6 e is a plan view of another arrangement in which plural heatsources are grouped in a different configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A number of exemplary embodiments of the invention are described hereinwith reference to the drawings, and demonstrate aspects of the inventionin different forms. The different embodiments are intended to representthe aspects separately in some instances, not all of the embodimentsincorporating all the alternatives mentioned herein. The drawings arenot necessarily comprehensive or drawn to scale. Certain features of theinvention are shown in schematic form in the interest of conciseness, orlarger or smaller than their preferred size for purposes of emphasis.

The invention has attributes that may be affected in some of theembodiments by the orientation of the associated apparatus in use. Theinvention also has attributes intended in some of the embodiments tofacilitate operation in different orientations.

In convection heating, for example, heating of a vapor decreases itsdensity and results in heated vapor currents with upward gradients;however heat and vapor also diffuse outwardly, including downwardly. Asto liquid, gravity can produce fluid flow with a downward gradient, butaccording to an aspect of the invention, liquid is movable by capillaryaction to flow in a direction that is not dependent on the tendency ofliquid to seek its lowest level.

These considerations must be taken into account in interpreting termsand statements in this disclosure that have implications of relativedirection or relative position such as “horizontal,” “vertical,” “up,”“down,” “top”and “bottom” as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.). Such directional termsshould not be assumed to define an orientation or relative position thatis necessary. Directional terms as used in this disclosure should beconstrued to refer to the orientation as then being described or asshown in the drawing figure under discussion, and not as a requirementor implication of a limitation to that particular direction ororientation, unless specifically stated or unless apparent from thecontext.

Similarly, internally relative terms such as “inwardly” versus“outwardly,” “longitudinal” versus “lateral,” etc., are intended torelate to one another, or to a center of area, mass, elongation,rotation, etc. As indicated in context appropriate, without limitationto only one such form of reference. Stated attachments such as“coupled,” “connected,” “interconnected,” and the like shall beconstrued to include a relationship wherein structures are secured orattached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, so as to support the pertinent functions with thedescribed structures.

Throughout the drawings, the same reference numbers are used to refer tothe same parts. Referring to FIG. 1, a single loop heat transfer circuit22 comprises a vessel defining an evaporator 24 in thermal engagementwith sources 28 of heat. The internal volume of the evaporator 24 iscoupled by a vapor line 32 to a condenser 34 that is configured torelease or further convey heat energy. In this example, condenser 34 hasfins 36 for operation as a convection-driven air heat exchanger. Aliquid return line 42 couples the condenser 34 to the evaporator 24,whereby a phase change working fluid contained in the heat transfercircuit is returned to the evaporator 24.

In a circulating loop, the working fluid is vaporized from its liquid tovapor phase at evaporator 24; conveyed as vapor through the vapor line32 to the condenser 34; condensed at the condenser from the vapor phaseto liquid, the condenser being kept at a lower temperature due to theescape of heat energy by convection; and caused to flow in the liquidphase from the condenser 34 back to the evaporator 24. Flow of vapor isdriven by diffusion from the area of vaporization through the volume ofthe system 22, which is partially evacuated and closed off as a sealedenvelope. Flow of liquid can be driven by gravity but preferably isdriven by capillary action to diffuse in the liquid phase through apicking material (not shown in FIG. 1) contained at least along internalwalls of the liquid return line 42.

As shown in exploded view in FIG. 2 and in section in FIG. 3, theevaporator 24 in this embodiment is a substantially rectangular boxhaving thermally conductive material such as aluminum or stainless steelsheet metal, at least along the surfaces to be placed in thermal contactwith heat sources 32, namely on the bottom 52 of evaporator 24. As shownin FIG. 1, the heat sources can comprise two integrated circuit packages28, 28, mounted at a space from one another on a printed circuit board45 and arranged such that thermally conductive walls of the evaporatorvessel 24 rest against the circuit packages 28 so as to absorb heat byconduction. Various known compounds such as phase change compounds (notshown) can be provided to fill any spaces between the circuit packageand the conductive wall of the evaporator vessel 24, in this case theunderside or bottom wall 52 of evaporator 24.

The side of the evaporator vessel 24 in contact with the heat sources 28needs to be thermally conductive. The other parts of the evaporator 24,and the respective vapor and liquid lines 32, 42, need not be thermallyconductive but nevertheless preferably are made of metal such as sheetmetal or tubing, or in the case of the box portion of evaporator 24,perhaps as a cast or stamped box unit 54. Use of metal for the parts isgenerally convenient for shaping, for heat conduction where needed, tofacilitate hermetic sealing of the elements to form a closed envelope,etc.

Regarding evaporator 24, FIG. 2 shows an arrangement in which thesidewalls and bottom are a cast metal unit 54 including standoff blocks55 that also provide for threaded bores for receiving fasteners such ascircuit-socket engaging spring clips (not shown). Portions of the bottom52 of evaporator 24 can be sheet metal that is stamped or bent to shape.Alternatively the bottom 52 can comprise multiple parts that areattached to one another and to the remaining parts of the evaporator,e.g., using solder, welding, adhesive or another technique. The lid part57 of evaporator 24 likewise is attached around the edges of the boxpart 54, e.g., by adhesive or solder around their abutting edges.

In the central area of bottom wall 52, the evaporator has a recessedreservoir or well 60 to which liquid working fluid from the condenser 34is returned to the evaporator 24 via a connecting opening 62 that isnear the bottom of the evaporator sidewall in the area of the well.Picking material 66 is provided at least along the sidewalls of the well60 and on the inside surfaces 68 of the bottom wall 52 of the evaporator24 in the zones over the integrated circuits or other heat sources 28.Thus, the working fluid in the well 60 is diffused in its liquid phaseby capillary action and flows up onto the surfaces that are adjacent tothe well 60 and over the heat sources 28. The liquid from the well 60thereby at least wets the entire inner bottom of the evaporator,including the areas over the heat sources 28. Depending on the level ofliquid working fluid in the evaporator, and assuming that the evaporatoris in a horizontal orientation, the working fluid can be pooled to adepth exceeding the depth of the well 60, thus providing relativelyshallower pooled areas over the heat sources 28. In any event, the heatsources tend to provide distinct spaced areas at which vaporization isconcentrated, as well as general heating of the working fluid leading tovaporization over its surface.

The heat sources 28 vaporize the liquid coolant at the inner bottom 68of the evaporator 24. The vaporizing working fluid moves by gaseousdiffusion through the available volume of the evaporator 24, namelybetween the whetted picking material on the bottom 68 and the undersideof the evaporator lid 57. A central turret 72 is provided over acomplementary-size hole 74 in the top wall or lid 57 of the evaporator24, and functions as a vapor accumulator. The turret 57 optionally canbe spaced inwardly from the lateral sidewalls 78 of the evaporator 24.The turret 57 has a soldered top lid 82 and a lateral opening to whichthe vapor line is coupled, also by soldering. The respective lids andthe vapor opening are best shown in FIG. 3. The turret allows theconnection to the vapor line 32 to be made at an elevation that is abovethe evaporator well 60, even if the evaporator is tipped laterally fromthe orientation shown in FIGS. 2 and 3. If the lateral inward spacebetween the sidewall 78 and the vapor accumulating turret 57 provides afluid space sufficient to accommodate the volume of fluid from well 60,the evaporator can be tipped laterally to 90° without causing liquidworking fluid to flow into the vapor line 32.

Referring again to FIG. 1, the condenser 34 comprises a stack of thinthermally conductive fins 86, preferably of sheet metal, providing alarge area of surface contact with the air. The condenser 34 couldprovide a heat exchanger for another fluid such as a current of water(not shown) but in the arrangement shown is arranged to heat air thatrises due to convection, producing a general upward air current in thearea of the condenser 34 for carrying heat away heat. This action couldbe assisted by a blower (not shown) suitably mounted to force air overthe fins 86. The fins can be separate sheets that are pressed andpreferably soldered to a longitudinal metal tube 88 for good thermalconduction resulting in a relatively cool inner surface for contact withand condensation of the vaporized working fluid. Alternatively, acorrugated or other irregular surface can be provided in an integralpiece of sheet material or the like. The longitudinal tube 88 forms asubstantially central passage through the condenser 34, capped at theends but for connections to the vapor and liquid lines (see FIGS. 4 and5), and in the case of a known-orientation arrangement, optionallyarranged at a downward tilt in the direction of flow. The vapor line 32is coupled to the condenser pipe 88 at one end and the liquid return 42line at the other end. The vapor line 32 has a relatively wider crosssection than the liquid return line 42. The tube 88 in the condenser canhave a progressively reducing diameter (not shown) proceeding throughthe condenser 34.

The picking material 66 is provided in the return line 42, andpreferably also lines the evaporator vessel 24 at least at the well andadjacent heating zones (the picking material being internal and notshown in FIG. 1). The picking material 66 can comprise fixed particlesor strands, a reticulated or sponge-like material having voids, acombination thereof, etc. In the case of particles or strands,individual bodies can be sintered or adhesively adhered or simplycompressed into place. The picking material is structured to provideinterstices or voids that are small compared to the dimensions of adroplet of the working fluid, which droplet could form due to thesurface tension of the liquid working fluid at the pressure andtemperature conditions in the envelope of the heat transfer device.Thus, the liquid phase working fluid tends to diffuse through thepicking material by capillary flow and does not depend on gravity.Capillary action ensures flow through the picking material from thecondenser 34 through the liquid return line 42 to the evaporator 24,without relying on gravity. However, in a situation where theorientation of the device is known and fixed, gravity can be employedwholly or partly as the operative force to cause flow of the workingfluid in the liquid phase, i.e., down a slope defined by the return line(see, e.g., FIG. 5).

The working fluid may be selected from a variety of well knownliquid/vapor phase change fluids selected and charged to a pressure thatcauses the phase change action to occur over the range of expectedtemperature conditions. The working fluid may include, for example,water, fluorinated hydrocarbon (e.g., Freon), ammonia, acetone,methanol, ethanol or combinations. Requirements for a suitable workingfluid are compatibility with the picking material on the internal wallsof the envelope, at least along the liquid return line and theevaporator adjacent to the well, wettability of the picking and wallmaterials, thermal stability, an operating vapor pressure that is notunduly high or low over the expected range of operating temperature, ahigh latent heat energy level stored and released during phase changes,high thermal conductivity, low liquid and vapor viscosities, highsurface tension and acceptable freezing or pour point.

The quantity and pressure conditions of the working fluid in the heattransfer device needs to be sufficient so that the picking materialadjacent to the fluid well in the evaporator, namely the pickingmaterial associated with the heat sources, is whetted at all conditionsover the range of operational conditions. This condition often can beachieved by inserting sufficient liquid phase working fluid to saturatethe picking material before partially evacuating and sealing off theenvelope of the device, for example by crimping and/or soldering a filltube, shown in FIGS. 4 and 5.

The choice of thermally conductive materials, the phase change workingfluid, the picking material and other aspects, are subject to somevariation. In one embodiment, the picking material comprisesmicro-encapsulated phase change material particles, namely havingadhered outer shells surrounding a phase change material. The shells aswell as the various thermally conductive tubes and walls as shown can bechosen from the class of materials suitable for heat transferapplications and known in the art, e.g., metals such as, silver, gold,copper, aluminum, titanium or their alloys. Polymeric materials are alsouseful, including materials useful in the electronics industry for heattransfer applications, such as thermoplastics (crystalline ornon-crystalline, cross-linked or non-cross-linked), thermosettingresins, elastomers or blends or composites thereof. Some examples ofuseful thermoplastic polymers are polyolefins such as polyethylene orpolypropylene, copolymers (including terpolymers, etc.) of olefins suchas ethylene and propylene, combinations thereof or with monomers such asvinyl esters, acids or esters of unsaturated organic acids or mixturesthereof, halogenated vinyl or vinylidene polymers such as polyvinylchloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidenefluoride and copolymers of these monomers with each other or with otherunsaturated monomers, polyesters, such as poly(hexamethylene adipate orsebacate), poly(ethylene terephthalate) and poly(tetramethyleneterephthalate), polyamides such as Nylon-6, Nylon-6,6, Nylon-6,10,Versamids, polystyrene, polyacrylonitrile, thermoplastic siliconeresins, thermoplastic polyethers, thermoplastic modified cellulose,polysulphones and the like.

In the embodiment of FIGS. 1-5, two heat sources 28 are mounted at theends of a rectilinear evaporator 24 that substantially matches thefootprint of the heat sources. The heat sources 28 are spaced by adistance that conveniently accommodates the well portion 60 of theevaporator 24 in the space between the heat sources (i.e., integratedcircuit packages mounted in sockets on a circuit board. This is acompact arrangement. Although in FIG. 1, the vapor and liquid returnlines 32, 42 are oriented to extend in opposite directions away from theevaporator 24, the particular route of the respective lines can bechanged for convenience in connecting the respective parts in theavailable space. The condenser 34 likewise can be shorter and wider, ororiented so that the flow path through the condenser varies from that ofthe exemplary arrangement shown.

Moreover, FIGS. 6 a through 6 e illustrate a number of alternative andcomparative arrangements. In FIG. 6 a, two heat sources 28 are spacedsymmetrically by the well 60 of an evaporator 24 (the connection lineparticulars not shown for clarity). This arrangement can be asymmetrical(FIG. 6 b), for example to complement the expected heat energy output ofunequal heat sources 28. The size, shape and position of the heatsources 28 can be varied, for example three different heat sources in awye arrangement shown in FIG. 6 c. Two or more heat sources 28 can sharean evaporation space or chamber, symmetrically as in FIG. 6 d orasymmetrically (FIG. 6 e). These configurations are examples and otherarrangements that vary in size, shape, heat source output, and otherfactors are possible.

In general, the heat transfer device 22 as disclosed is configured forremoving heat energy from a plurality of heat loads 28. A heat exchangestructure is provided containing a working fluid in a substantiallyclosed envelope defining at least one evaporator 24 and at least onecondenser 34 coupled to provide a circulating path for the workingfluid, through vaporization of a liquid phase of the working fluid atthe evaporator 24, condensation of a vapor phase of the working fluid atthe condenser 34, and return of the working fluid from the condenser tothe evaporator. According to an inventive aspect, the evaporator 24defines a reservoir 60 for the liquid phase of the working fluid, andthe evaporator 24 comprises at least two spaced evaporation points forapplication of heat energy from distinct ones of the heat loads 28, thetwo or more spaced evaporation points being commonly supplied with theliquid phase of the working fluid from the reservoir 60. The reservoir60 in the embodiment of FIGS. 1-5 is defined at least partly by adepression in a bottom wall of the evaporator 24, preferably betweenevaporation points at which the heat sources 28 contact the evaporator24. In other embodiments, the reservoir can be defined by a flatreservoir bottom.

In the embodiments shown, the evaporator 24 consists essentially of anintegral vessel comprising thermally conductive material, said spacedevaporation points being located at spaced positions on the integralvessel, such as distinct areas of a bottom wall 68. It is also possibleto embody the invention in a manner in which two heating zones are morediscretely arranged but nevertheless share a reservoir or supply ofworking fluid and feed vapor to a common vapor accumulator 72 or vaporline 32, thereby functioning as one evaporator driven by two or moreheat sources 28 that are potentially at different temperatures.Furthermore, the invention does not exclude the possibility of anarrangement, as otherwise shown in the drawings, wherein two or moresuch multiple heating zone evaporators are coupled in a heat transferloop.

In the preferred arrangements, the reservoir 60 of working fluid isdisposed between at least two such spaced evaporation points and feedsliquid phase working fluid to the evaporation points for vaporization.This can be efficiently accomplished without relying on orientation bycoupling the fluid in the well or reservoir to one or both of theevaporation points via a picking material 66 supporting capillary flowof the liquid phase of the working fluid. Alternatively or in addition,the well 60 could be arranged routinely to overflow onto flat, sloped,wicked or other surfaces defining the evaporation points.

In the arrangements shown in FIGS. 1-6 b, the working fluid liquidreservoir is defined by at least one recessed well in the enclosure thatdefines the evaporator, namely in the form of an integral box-likestructure with a low point in the bottom for the well 60 and theevaporation points being located on inside bottom walls 68 of theenclosure that are parallel to the bottom of the well 60 and adjacent tothe well. In other particular arrangements, the well could be a curvedbowl. The adjacent walls 68 also can slope upwardly from an intermediatearea defining a central low point in a vee arrangement. Other particularshapes are likewise useful.

The spaced evaporation points are placed at different positions in theevaporator around the recessed well 60, especially at differentpositions around a perimeter of the recessed well and at an elevationhigher than a bottom of the recessed well. In one arrangement, theevaporation points are in subsections of the evaporator that are more orless isolated because the points are in corridors or chambers thatradiate outward from the well 60 or at least are on different pointsaround a perimeter of the well. In this way, the temperatures maintainedby the heat sources at the respective evaporation points are related tothe heat outputs and temperatures of the sources 28, as opposed tohaving the hotter source effectively operated at a lower temperaturethan it otherwise might operate, due to conduction of heat energy fromits evaporation point to nearby evaporation points of other normallycooler or lower heat energy sources.

In several of the illustrated embodiments, the enclosure compriseschambers radiating from a center, optionally a recessed well 60. Thespaced evaporation points are placed on walls of the chambers thatradiate, particularly bottom walls but also potentially the top, side orend walls of these chambers. The chambers can be symmetrically orasymmetrically arranged relative to one another and can be evenly orunevenly placed in relation to one another, the chambers and/or therespective energy outputs of the heat sources, and can comprise one ormore than one source per identifiable unit of space or area.

It is to be understood that the present invention is by no means limitedonly to the particular constructions herein disclosed and shown in thedrawings, but also comprises any modifications or equivalents within thescope of the claims.

1. A heat transfer device for removing heat energy from a plurality ofheat loads, comprising: a heat exchange structure containing a workingfluid in a substantially closed envelope defining at least oneevaporator and at least one condenser coupled to provide a circulatingpath for the working fluid, through vaporization of a liquid phase ofthe working fluid at the evaporator, condensation of a vapor phase ofthe working fluid at the condenser, and return of the working fluid fromthe condenser to the evaporator; wherein the evaporator defines areservoir for the liquid phase of the working fluid, and the evaporatorcomprises at least two spaced evaporation points for application of heatenergy from distinct ones of the heat loads, said two spaced evaporationpoints being commonly supplied with the liquid phase of the workingfluid from the reservoir.
 2. The heat transfer device according to claim1, wherein the evaporator consists essentially of an integral vesselcomprising thermally conductive material, said spaced evaporation pointsbeing located at spaced positions on the integral vessel.
 3. The heattransfer device according to claim 1, wherein the reservoir is disposedbetween said at least two spaced evaporation points.
 4. The heattransfer device according to claim 1, wherein the reservoir is coupledto at least one of the evaporation points by a picking materialsupporting capillary flow of the liquid phase of the working fluid. 5.The heat transfer device according to claim 1, wherein the reservoir isdefined by at least one recessed well in an enclosure defining theevaporator, said evaporation points being located on walls of theenclosure.
 6. The heat transfer device according to claim 4, wherein thespaced evaporation points are placed at different positions in theevaporator around the recessed well.
 7. The heat transfer deviceaccording to claim 6, wherein the spaced evaporation points are placedat different positions around a perimeter of the recessed well.
 8. Theheat transfer device according to claim 6, wherein the spacedevaporation points are placed at different positions adjacent to therecessed well and at an elevation higher than a bottom of the recessedwell.
 9. The heat transfer device according to claim 5, wherein theenclosure comprises a chambers radiating from the recessed well and thespaced evaporation points are placed on walls of the chambers.
 10. Theheat transfer device according to claim 9, wherein the chambers areasymmetrically arranged relative to one another.
 11. The heat transferdevice according to claim 9, wherein the evaporation points are unevenlydistributed in the chambers.
 12. The heat transfer device according toclaim 11, wherein the evaporation points are spaced to complement unevenratings of the heat loads for respective ones of the evaporation points.13. The heat transfer device according to claim 9, wherein at least oneof said chambers has at least two of said evaporation points therein.14. The heat transfer device according to claim 5, wherein at least twoof the evaporation points abut the recessed well at stepped edges of anunderside of the evaporator, surrounding the recessed well, whereby theevaporation points are supplied commonly from the recessed well, andfurther comprising a vapor outlet placed substantially over the recessedwell, whereby vapor from the evaporation points diffuses commonly intothe vapor outlet.